KR101552750B1 - Parametric stereo conversion system and method - Google Patents

Abstract

A system is provided for generating parametric stereo data from phase modulated stereo data. The phase difference system receives the left channel data and the right channel data and determines the phase difference between the left channel data and the right channel data. The phase difference weighting system receives the phase difference data and generates weighted data for adjusting the left channel amplitude data and the right channel amplitude data based on the phase difference data. The amplitude changing system adjusts the left channel amplitude data and the right channel amplitude data using the weighted data to remove the phase data from the left channel data and the right channel data.

Description

[0001] PARAMETRIC STEREO CONVERSION SYSTEM AND METHOD [0002]

This application claims priority to U.S. Provisional Application No. 60 / 965,227, filed August 17, 2007, entitled " Parametric Stereo Conversion System and Method, " which application is incorporated herein by reference for all purposes.

The present invention relates to the field of audio coders and more particularly to a method and apparatus for compensating amplitude data for variations in phase data without the generation of audio artifacts or other noise that may occur when phase data is missing, Channel audio data having amplitude data and phase data so that only amplitude data is transmitted per channel of the channel data.

Multi-channel audio coding techniques for removing phase data from audio signals including phase data and amplitude data are known in the art. These techniques include parametric stereos, which use the amplitude difference between the left channel signal and the right channel signal to be used to simulate a stereophonic sound that will typically include phase information. This parametric stereo does not allow the listener to experience a stereophonic sound with a depth of field that would have been experienced if the phase data was also included in the signal, Provides a certain depth of improvement in sound quality compared to a simple monaural sound.

One problem in converting multi-channel audio data including amplitude data and phase data into multi-channel audio data containing only amplitude data is the proper processing of phase data. If the phase data is simply detected, an audio artifact will be generated that causes the listener to be uncomfortable to hear, resulting in amplitude alone data. Some systems, such as the Advanced Audio Coding (AAC) system, utilize the sideband information used by the receiver to compensate for the elimination of phase data, but such systems require the user to process sideband data , And also suffer from problems that may arise when the noise signal is introduced into the sideband data, which can create an unpleasant audio artifact. In addition, attempts to transmit sideband data for high frequency phase variations when a low bit rate transmission process is used can generate audio artifacts.

According to the present invention there is provided a system for processing a multi-channel audio signal to compensate amplitude data for phase data, overcoming known problems in converting audio data having phase data and amplitude data into audio data having only amplitude data, Method is provided.

In particular, a system and method are provided for processing a multi-channel audio signal to compensate amplitude data for phase data, eliminating the need for sideband data and providing compensation for audio artifacts that may occur during the conversion process.

According to an exemplary embodiment of the present invention, a system is provided for generating parametric stereo data from phase modulated stereo data. The phase difference system receives the left channel data and the right channel data and determines the phase difference between the left channel data and the right channel data. The phase difference weighting system receives the phase difference data and generates weighted data for adjusting the left channel amplitude data and the right channel amplitude data based on the phase difference data. The amplitude changing system adjusts the left channel amplitude data and the right channel amplitude data using the weighted data to remove the phase data from the left channel data and the right channel data.

The present invention provides a number of important technical advantages. One important technical advantage of the present invention is that the amplitude data is flattened based on variations in the phase data to avoid generation of audio artifacts that may occur when the low bit rate amplitude data is adjusted to include high frequency phase variations, And a system and method for processing a multi-channel audio signal to compensate amplitude data for phase data.

Those skilled in the art, upon reading the following detailed description in conjunction with the drawings, will better understand the advantages and features of the present invention, along with other important aspects of the present invention.

A system for generating parametric stereo data from phase-modulated stereo data may be provided.

1 is a diagram of a system for converting multi-channel audio data having both phase data and amplitude data, such as parametric stereo, into multi-channel audio data utilizing only amplitude data, in accordance with an exemplary embodiment of the present invention .
Figure 2 is a plot of phase difference weighting factors in accordance with an exemplary embodiment of the present invention.
3 is a diagram of a coherence spatial adjustment system in accordance with an exemplary embodiment of the present invention.
4 is a diagram of a method for parametric coding in accordance with an exemplary embodiment of the present invention.
5 is a diagram of a system for dynamic phase trend correction in accordance with an exemplary embodiment of the present invention.
6 is a diagram of a system for performing spectral planarization in accordance with an exemplary embodiment of the present invention.
Figure 7 is a diagram of a system for power compensated intensity re-panning in accordance with an exemplary embodiment of the present invention.

In the following detailed description, like parts throughout the specification and drawings are denoted by like reference numerals. Figures in the figures may not be actual scale and some components may be shown in approximate or simplified form to facilitate clarity and simplicity and may be identified by their commercial names.

1 illustrates a system 100 for converting multi-channel audio data having both phase data and amplitude data into multi-channel audio data utilizing only amplitude data, such as parametric stereo, in accordance with an exemplary embodiment of the present invention. Fig. System 100 identifies the phase difference in the left and right channel sound data and converts the phase difference to an amplitude difference to produce stereophonic image data using only intensity data or amplitude data. Likewise, additional channels may also be used or otherwise used where appropriate.

The system 100 receives time-domain right channel audio data in the time-frequency conversion system 102 and time-domain left channel audio data in the time-frequency conversion system 104. In one exemplary embodiment, the system 100 may be implemented in hardware, software, or a suitable combination of hardware and software, and it may be implemented as a digital system processor, a general purpose processing platform, or one or more Software systems. As used herein, a hardware system may include discrete components, an integrated circuit, an application specific integrated circuit, a field programmable gate array, or any other suitable combination of hardware.

A software system may include one or more software applications or two or more processors, or one or more objects, agents, threads, code lines, subroutines, separate soft applications , Two or more lines of code, or other appropriate software structures. In one exemplary embodiment, a software system includes one or more lines of code or other suitable software structures, such as an operating system, operating in a general purpose software application, and one or more lines of code And other suitable software structures.

The time-frequency conversion system 102 and the time-frequency conversion system 104 convert the right-channel time-domain audio data and the left-channel time-domain audio data into frequency-domain data, respectively. In one exemplary embodiment, the frequency domain data includes a frame of frequency data captured over the sample period, such as bins of frequency data of 1,024 during an appropriate time period, such as 30 milliseconds. can do. The bins of the frequency data may be evenly spaced over a predetermined frequency range, such as 20 kHz, and may be coherent in predetermined bands such as bark, equivalent rectangular bandwidth (ERB) Or otherwise distributed appropriately.

The time-frequency conversion system 102 and the time-frequency conversion system 104 are coupled to the phase difference system 106. As used herein, the terms " coupled "and its like terms (e. G.," Coupled "or" coupled ") refer to a physical connection (such as a wire, optical fiber, Virtual connections (such as through randomly designated memory locations of devices or hypertext transfer protocol (HTTP) links), logical connections (such as through one or more semiconductor devices in an integrated circuit), or other suitable Connections. In one exemplary embodiment, the communication medium may be a network or other suitable communication medium.

The phase difference system 106 determines the phase difference between the frequency bins in the frames of frequency data generated by the time-frequency conversion system 102 and the time-frequency conversion system 104. These phase differences will be normally recognized by the listener and represent phase data that improves the stereophonic quality of the signal.

The phase difference system 106 is coupled to a buffer system 108 that includes an N-2 frame buffer 110, an N-1 frame buffer 112, and an N frame buffer 114. In one exemplary embodiment, the buffer system 108 may include an appropriate number of frame buffers to store the phase difference data from the desired number of frames. The N-2 frame buffer 110 receives the phase difference data received from the phase difference system 106 for the second previous data frames transformed by the time-frequency transform system 102 and the time- / RTI > Similarly, the N-1 frame buffer 112 stores the phase difference data for the previous phase difference data frames from the phase difference system 106. [ The N frame buffer 114 stores the current phase difference data for the current frames of the phase difference generated by the phase difference system 106. [

The phase difference system 116 is coupled to the N-2 frame buffer 110 and the N-1 frame buffer 112 and determines the phase difference between the two sets of phase difference data stored in these buffers. Similarly, phase difference system 118 is coupled to N-1 frame buffer 112 and N frame buffer 114 and determines the phase difference between the two sets of phase difference data stored in these buffers. Likewise, additional phase difference systems can be used to generate phase differences for an appropriate number of frames stored in the buffer system 108.

Phase difference system 120 is coupled to phase difference system 116 and phase difference system 118, receives phase difference data from each system, and determines the total phase difference. In this exemplary embodiment, to identify frequency bins having a larger phase difference and frequency bins having a smaller phase difference, the phase difference for three consecutive frequency data frames is determined. Additional phase difference systems may also be used or alternatively may be used to determine the total phase difference for a predetermined number of phase difference data frames.

Phase difference buffer 122 stores phase difference data from phase difference system 120 for the previous set of three frames. Similarly, if the buffer system 108 includes more than three frame differences, the phase difference buffer 122 may store additional phase difference data. The phase difference buffer 122 also includes a set generated from the frames N-4, N-3 and N-2, a set generated from the frames N-3, N-2 and N- Additional previous phase difference data sets, such as a set generated from frames N-2, N-1, N, a set generated from frames N-1, N, N + Or may alternatively store such data. ≪ RTI ID = 0.0 >

The phase difference weighting system 124 receives the buffered phase difference data from the phase difference buffer 122, receives the current phase difference data from the phase difference system 120, and applies a phase difference weighting factor. In one exemplary embodiment, frequency bins representing a high degree of phase difference are given weighting factors that are smaller than frequency bins representing a consistent phase difference. In this manner, the frequency difference data is used to flatten the amplitude data to remove changes from frequency bins representing the high degree of phase difference between successive frames and to provide emphasis on frequency bins representing low phase differences between successive frames Can be used. This leveling is especially introduced when the low bit rate audio data is being processed or being generated by conversion from audio data having phase data and amplitude data to audio data having only amplitude data, such as parametric stereo data Which can help reduce or eliminate audio artifacts that can occur.

The amplitude changing system 126 receives the phase difference weighting factor data from the phase difference weighting system 124 and provides amplitude changing data from the time-frequency transforming system 102 and the time-frequency transforming system 104 to the transformed left channel and right Channel data. In this way, the current frame frequency data for the left and right channel audio is modified to adjust the amplitude to correct the phase difference, which allows panning between the left and right amplitude values to be used to generate the stereophonic sound. In this way, the phase difference between the left and right channels is flattened and converted into amplitude change data in order to simulate a stereo channel sound or other multi-channel sound only by the amplitude without the phase data needing to be transmitted. Similarly, to utilize data from a set of frequency data frames (N-1, N, N + 1), or other suitable data sets, the buffer system may be used to buffer the current frame of frequency data being modified . The amplitude modification system 126 may also contraction or expand the amplitude difference between two or more channels for a predetermined frequency bands, a group of frequency bins, or other suitable frequency bands to narrow or broaden the apparent stage for the listener The amplitude difference between the channels can be contracted or expanded.

The frequency-to-time conversion system 128 and the frequency-to-time conversion system 130 receive the changed amplitude data from the amplitude varying system 126 and convert the frequency data into a time signal. In this way, the near-channel and right-channel data generated by the frequency-to-time conversion system 128 and the frequency-to-time conversion system 130 for simulating stereo data using only the intensity are each in phase but with different amplitudes , Whereby the phase data need not be stored, transmitted, or otherwise processed.

In operation, in order to reduce the amount of data that needs to be transmitted to produce stereo phonetic or other multi-channel audio data or other multi-channel audio data, the system 100 includes multi-channel audio data And generates multi-channel audio data having only amplitude data. System 100 compensates for variations in frequency data in a manner that reduces effects from high frequency phase fluctuations, so that when the audio data including phase and amplitude data is converted to audio data that includes only amplitude data Remove audio artifacts that can be. In this way, audio artifacts that could be introduced when the available bit rate for transmission of audio data was lower than the bit rate needed to accurately represent the high frequency phase data, if it were through other schemes, is eliminated.

2 is a diagram of phase difference weighting factors 200A, 200B in accordance with an exemplary embodiment of the present invention. The phase difference weighting factors 200A and 200B show exemplary leveled weighting factors to be applied to the amplitude data as a phase variation function. In one exemplary embodiment, in order to flatten out the potential noise or other audio artifacts that would cause parametric stereo data or other multi-channel data to inappropriately represent the stereo sound, frequency bins that show a high degree of phase variation Is weighted with a lowered equalized weighting factor than frequency bins showing a lower degree of phase variation. In one exemplary embodiment, phase difference weighting factors 200A and 200B may be applied by phase difference weighting system 124 or other suitable system. The amount of weight can be changed to achieve an expected reduction in bit rate for audio data. For example, if a high degree of data reduction is required, the weights given to the frequency bins representing the high degree of phase variation can be significantly reduced, such as in the asymptotic manner shown in phase difference weighting factor 200A, A weight given to frequency bins representing a higher degree of phase variation can be reduced to a smaller value, such as by using a phase difference weighting factor 200B.

3 is a diagram of a coherence spatial adjustment system 300 in accordance with an exemplary embodiment of the present invention. Coherence spatial adjustment system 300 may be implemented in hardware, software, or a suitable combination of hardware and software, which may be implemented in one or more systems operating on a general purpose processing platform, or in one or more discrete devices, Systems.

Coherence spatial adjustment system 300 provides an example of an exemplary spatial adjustment system, but other suitable frameworks, systems, processes, or architectures for implementing spatial adjustment algorithms may also be utilized, or alternatively, Can be used.

Coherence spatial adjustment system 300 changes spatial aspects of a multi-channel audio signal (i. E., System 300 shows a stereo adjustment system) to reduce artifacts during audio compression. The phase spectrum of the stereo input spectrum is first differentiated by the subtractor 302 to generate a differential phase spectrum. The differential phase spectrum is weighted by a weighting factor Y (K) = B ₁ X (K) + B ₂ X (K-1) - A ₁ Y (K-1)

here:

Y (K) = flattened frequency bin K amplitude;

Y (K-1) = flattened frequency bin K-1 amplitude;

X (K) = frequency bin K amplitude;

X (K-1) = frequency bin K-1 amplitude;

B ₁ = weighting factor;

B ₂ = weighting factor;

A ₁ = weighting factor; And

B ₁ + B ₂ + A ₁ = 1.

The weighting factors, B ₁ , B ₂ , A ₁ , may be determined based on observations, system design, or other appropriate factors. In one exemplary embodiment, the weighting factors, B ₁ , B ₂ , A ₁ , are fixed for all frequency bins. Similarly, the weighting factors, B ₁ , B ₂ , A ₁ , may be changed based on a group of bark or other suitable frequency bins.

The weighted difference phase signal is then divided by 2 and subtracted by the subtractor 308 from the input phase spectrum 0 and summed with the input phase spectrum 1 by the adder 306. [ The outputs of the subtractors 308 and 306 are the output adjusted phase spectrum 0 and the output adjusted phase spectrum 1, respectively.

In operation, the coherence spatial adjustment system 300 has the effect of generating a mono phase spectrum band, such as for use in parametric stereos.

4 is a diagram of a method 400 for parametric coding in accordance with an exemplary embodiment of the present invention. The method 400 begins at step 402 where the N audio data channels are transformed into the frequency domain. In one exemplary embodiment, the left channel stereo data and the right channel stereo data may each be transformed into a frame of frequency domain data over a predetermined period of time, such as using a Fourier transform or other appropriate transformation. The method then proceeds to step 404.

In step 404, the phase difference between the channels is determined. In one exemplary embodiment, the frequency bins of the left and right channel audio data may be compared to determine the phase difference between the left and right channels. The method then proceeds to step 406.

In step 406, the phase difference data for the frame is stored in the buffer. In one exemplary embodiment, the buffer system may include a predetermined number of buffers for storing phase difference data, the buffers may be dynamically allocated, or other suitable processes may be used. The method then proceeds to step 408.

At step 408, it is determined whether M data frames are stored in the buffer. In one exemplary embodiment, M may be equal to 3, or may be any other appropriate number of years to allow for the planarization to be performed between a desired number of frames. If, at step 408, it is determined that M data frames are not stored, the method returns to step 402. Otherwise, the method proceeds to step 410.

In step 410, the phase difference between the M-1 frame and the M frame is determined. For example, if M equals 3, the phase difference between the second frame and the third frame of data is determined. The method then proceeds to step 412 where the phase difference data is buffered. In one exemplary embodiment, a predetermined number of buffers may be created in hardware or software, and the buffer system may dynamically allocate buffer data storage areas, or other suitable processes may be utilized. The method then proceeds to step 414 where M is decremented by one. The method then proceeds to step 416 of determining whether M is equal to zero. For example, if M equals zero, all buffered data frames have been processed. If it is determined that M is not equal to 0, the method returns to step 402. [ Otherwise, the method proceeds to step 418.

In step 418, the phase difference between the buffered frame phase difference data is determined. For example, if two phase difference data frames are stored, the difference between the two frames is determined. Likewise, differences between three, four, or any other suitable number of phase difference data frames may be used. The method then proceeds to step 420 where the multi-frame difference data is buffered. The method then proceeds to step 422.

At step 422, a determination is made whether a predetermined number of multi-frame buffer values are stored. If it is determined that a predetermined number of multi-frame buffer values are not stored, the method returns to step 402. Otherwise, the method proceeds to step 424.

In step 424, phase difference data for the previous multi-frame buffer and the current multi-frame buffer are generated. For example, if there are two multi-frame buffered data values, the phase difference between the two multi-frame buffers is determined. Similarly, if N is greater than 2, the phase difference between the previous multi-frame buffer and the current multi-frame buffer can also be determined. The method then proceeds to step 426.

In step 426, a weighting factor based on the phase difference data is applied to each frequency bin in the current frame, previous frame, or other appropriate frame of frequency data. For example, to reduce other information, audio artifacts, or noise that represent phase data that can produce audio artifacts in parametric stereo data if the phase data is discarded or otherwise discarded, Can apply a higher weight to the amplitude values for frequency bins that exhibit small phase fluctuations and can less emphasize frequency bins that exhibit high phase fluctuations. The weighting factors can be selected based on a predetermined reduction in audio data transmission bit rate, which can also vary based on the group of frequency bins or frequency bins, or alternatively can vary as such. The method then proceeds to step 428.

In step 428, the weighted frequency data for the left channel data and the right channel data is transformed from the frequency domain to the time domain. In one exemplary embodiment, a planarization process may be performed on a current set of frames of audio data, based on sets of previous frames of audio data. In another exemplary embodiment, a planarization process may be performed on a previous set of frames of audio data, based on previous frames of audio data and subsequent sets of frames. Likewise, other suitable processes may also be used or alternatively may be used. In this manner, the channels of audio data can be generated without requiring storage or transmission of phase data, and when the frequency of phase variations between channels exceeds the frequency that can be accommodated by the available transmission channel bandwidth In order to simulate multichannel sound without the generation of an audio artifact, it represents a parametric multi-channel quality in which the phase data is removed but the phase data is converted to amplitude data.

In operation, the method 400 allows parametric stereo or other multi-channel data to be generated. The method 400 may also be used to store stereo or other multi-channel sounds, such as stereo or other multi-channel sound, to preserve aspects of stereo phonics or other multi-channel sound without requiring that the phase relationship between the left and right or other multi- Eliminates frequency differences between channel data, and converts these frequency variations into amplitude variations. In this manner, existing receivers can be used to generate phase-compensated multi-channel audio data without the need for sideband data or other data required by the receiver to compensate for the elimination of phase data.

5 is a diagram of a system 500 for dynamic phase trend correction in accordance with an exemplary embodiment of the present invention. The system 500 may be implemented in hardware, software, or a suitable combination of hardware and software, which may be one or more software systems operating on a general purpose processing platform.

The system 500 includes a left temporal signal system 502 and a right temporal signal system 504 that provide left and right channel time signals generated or received from a stereophonic sound source, . The short-range Fourier transform systems 506 and 508 are coupled to the left temporal signal system 502 and the right temporal signal system 504, respectively, and perform time-frequency domain transform of time signals. Other transforms, such as Fourier transforms, discrete cosine transforms, or other suitable transforms may also be used, or alternatively may be used.

Outputs from the short-range Fourier transform systems 506 and 508 are provided to the three-frame delay systems 510 and 520, respectively. The amplitude outputs of the short-range Fourier transform systems 506 and 508 are provided to the amplitude systems 512 and 518, respectively. The phase outputs of the short-range Fourier transform systems 506 and 508 are provided to the phase systems 514 and 516, respectively. Additional processing may be performed by the amplitude systems 512 and 518 and the phase systems 514 and 516 and these systems may provide respective non-processed signals or data.

The critical band filter banks 522 and 524 receive the amplitude data from the amplitude systems 512 and 518, respectively, and filter the predetermined frequency data bands. In one exemplary embodiment, the critical band filter banks 522 and 524 include a psychoacoustic filter (not shown) that groups frequency bins based on the perceptual energies of human auditory responses and frequency bins, such as the frequency scale of Bark linearly spaced frequency bins may be grouped into non-linear groups of frequency bins based on a psycho-acoustic filter. In one exemplary embodiment, the Bark frequency scale may have a range of 1 to 24 barks, corresponding to the first 24 human auditory threshold bands. Exemplary Bark band edges are 0, 100, 200, 300, 400, 510, 630, 770, 920, 1080, 1270, 1480, 1720, 2000, 2320, 2700, 3150, 3700, 4400, 5300, 6400, 7700, 9500, 12000, 15500 Hz. Exemplary Bark band centers are 50, 150, 250, 350, 450, 570, 700, 840, 1000, 1170, 1370, 1600, 1850, 2150, 2500, 2900, 3400, 4000, 4800, 5800, 7000, 8500, 10500, 13500 Hz.

In this exemplary embodiment, the Bark frequency scale is defined only up to 15.5 kHz. Thus, the highest sampling rate for this exemplary Bark scale is the Nyquist limit, or 31 kHz. A 25 th exemplary Bark band extending above 19 kHz (sum of the 24th Bark band edge and the 23rd critical bandwidth) can be utilized so that a sampling rate of 40 kHz can be used. Likewise, by adding a value of 20500 and a value of 27000, additional Bark band edges can be utilized so that a sampling rate of up to 54 kHz can be used. Human auditory sense generally does not extend beyond 20 kHz, but audio sampling rates higher than 40 kHz are practically universal.

The time planarization system 526 receives the filtered amplitude data from the critical band filter banks 522 and 524, receives the phase data from the phase systems 514 and 516, and performs time flattening of the data. In one exemplary embodiment, the phase delta between the left and right channels can be determined, for example, by applying the following algorithm or other appropriate methods:

here:

P = phase difference between left and right channels;

X _l = left stereo input signal;

X _r = right stereo input signal;

m = current frame; And

K = frequency bin index.

The delta planarization factor can then be determined, for example, by applying the following algorithm or other appropriate methods:

here:

? = planarization coefficient;

x = parameter for controlling the planarization bias (generally 1, may be greater than 1 to exaggerate panning and less than 1 to reduce panning);

P = phase difference between left and right channels;

m = current frame; And

K = frequency bin index.

The spectral dominant smoothing factor can then be determined, for example, by applying the following algorithm or other suitable methods:

here:

D = flattening factor;

C = critical band energy (output of filter banks);

N = perceptual bands (number of filter bank bands);

m = current frame; And

b = frequency band.

The phase delta signal can then be flattened, for example, by applying the following algorithm or other suitable methods:

here:

? = planarization coefficient;

D = spectral dominant weight remapped to linear equivalent frequencies; And

P = phase difference between left and right channels.

To reduce spectral fluctuations that can create unwanted audio artifacts, a spectrum planarization system 528 receives the output from the time planarization system and performs spatial planarization of the output.

Phase response filter system 530 receives the outputs of spectral flattening system 528 and time delay systems 510 and 520 and performs phase response filtering. In one exemplary embodiment, the phase response filter system 530 may calculate phase shift coefficients by applying, for example, the following equation or other appropriate methods:

here:

Y _l = Left channel complex filter coefficient;

Y _r = right channel complex filter coefficient; And

X = input phase signal.

The input signal can then be filtered, for example, by applying the following algorithm or other suitable methods:

here:

Y _l = left complex coefficient;

Y _r = right complex coefficient;

X _l = left stereo input signal;

X _r = Right stereo input signal;

H _l = left phase shifted result; And

H _r = right phase shifted result; And

The short term inverse Fourier transform systems 532 and 534 receive the left and right phase shifted data from the phase response filter system 530, respectively, and perform short term inverse Fourier transform on the data. Other transforms, such as inverse Fourier transforms, inverse discrete cosine transforms, or other suitable transforms may also be used, or alternatively may be used.

The left time signal system 536 and the right time signal system 538 provide left and right channel signals, such as stereo phonetic signals for transmission over low bit rate channels. In one exemplary embodiment, the processed signals provided by the left temporal signal system 536 and the right temporal signal system 538 are used to remove audio components that would otherwise have generated unwanted audio artifacts Can be used to provide stereo sound data with improved audio quality at low bit rates.

6 is a diagram of a system 600 for performing spectral flattening in accordance with an exemplary embodiment of the present invention. The system 600 may be implemented in hardware, software, or any suitable combination of hardware and software, which may be one or more software systems operating on a general purpose processing platform.

The system 600 includes a phase signal system 602 that is capable of receiving a processed phase signal, e.g., from a time planarization system 502 or other suitable systems. The cosine system 604 and the sign system 606 generate cosine and sine values of the phase of the processed phase signal, respectively. The zero phase filters 608 and 610 perform zero phase filtering of cosine and sine values, respectively, and the phase estimation system 612 receives the zero phase filtered cosine and sine data and generates the spectrally flattened signal.

In operation, the system 600 receives a phase signal having a phase value varying from pi to-pi, which may be difficult to filter to reduce high frequency components. The system 600 converts the phase signal to sine and cosine values so that a zero phase filter can be used to reduce the high frequency components.

FIG. 7 is a diagram of a system 700 for power-compensated intensity re-panning in accordance with an exemplary embodiment of the present invention. The system 700 may be implemented in hardware, software, or a suitable combination of hardware and software, which may be one or more software systems operating on a general purpose processing platform.

System 700 includes a left temporal signal system 702 and a right temporal signal system 704 that provide left and right channel time signals generated or received from a stereophonic sound source, . The short-range Fourier transform systems 706 and 710 are coupled to the left temporal signal system 702 and the right temporal signal system 704, respectively, and perform time-frequency domain transform of time signals. Other transforms, such as Fourier transforms, discrete cosine transforms, or other suitable transforms may also be used, or alternatively may be used.

The strength re-panning system 708 performs strength re-panning of the left and right channel converted signals. In one exemplary embodiment, the strength re-panning system 708 may apply the following algorithm or other appropriate processes:

here:

M _l = left channel intensity panned signal;

M _r = right channel intensity panned signal;

X _l = left stereo input signal;

X _r = Right stereo input signal; And

β = nonlinear option to compensate for perceived collapse of the stereo image due to elimination of the phase difference between the left and right signals (this is typically 1, may be greater than 1 to increase panning, or less than 1 to reduce panning) .

The composite signal generation system 712 generates a composite signal from the left and right channel conversion signals and the left and right channel intensity panned signals. In one exemplary embodiment, the composite signal generation system 712 may apply the following algorithm or other appropriate processes:

here:

C _l = a left channel composite signal including an original signal mixed with an intensity panned signal determined by a frequency dependent window (W);

C _r = right channel composite signal including original signal mixed with intensity panned signal determined by frequency dependent window (W);

X _l = left stereo input signal;

X _r = right stereo input signal;

M _l = left intensity panned signal;

M _r = right intensity panned signal;

W = a frequency dependent window that determines the mixture at different frequencies (a variable bypassing frequencies; if 0, only the original signal, greater than 0 (e.g., 0.5), a mixture of the original signal and the intensity panned signal .

The power compensation system 714 generates a power compensated signal from the left and right channel conversion signals and the left and right channel composite signals. In one exemplary embodiment, the power compensation system 714 may apply the following algorithm or other suitable processes:

here:

Y _l = left channel power compensated signal;

Y _r = right channel power compensated signal;

C _l = left channel composite signal;

C _r = right channel composite signal;

X _l = left channel stereo input signal; And

X _r = right channel stereo input signal.

The short term inverse Fourier transform systems 716 and 718 receive power compensated data from the power compensation system 714 and perform a short term inverse Fourier transform on the data. Other transforms, such as inverse Fourier transforms, inverse discrete cosine transforms, or other suitable transforms may also be used, or alternatively may be used.

The left temporal signal system 720 and the right temporal signal system 722 provide left and right channel signals, such as stereo phonetic signals for transmission over a low bit rate channel. In one exemplary embodiment, the processed signals provided by the left temporal signal system 720 and the right temporal signal system 722 are used to remove audio components that would otherwise generate unwanted audio artifacts Can be used to provide stereo sound data with improved audio quality at low bit rates.

Although illustrative embodiments of the systems and methods of the present invention have been described in detail herein, those skilled in the art will also appreciate that various alternative constructions and variations can be made to the system and method without departing from the scope and spirit of the appended claims. You will know that you can.

102: time-frequency conversion system, 104: time-frequency conversion system
106: phase difference system, 128: frequency-time conversion system
130: frequency-time conversion system, 126: amplitude change system
124: phase difference weighting system, 108: buffer system
110: N-2 frame buffer, 112: N-1 frame buffer
114: N frame buffer, 116, 118, 120: phase difference system
122: phase difference buffer,
502, 536: Left time signal system,
504, 538: Right time signal system,
510, 520: three frame delay system, 512, 518: amplitude system
514, 516: phase system, 522, 524: critical band filter bank
526: time planarization system, 528: spectrum planarization system
530: phase response filter, 602: phase signal
608, 610: zero phase filter, 612: phase estimation system
702, 720: Left time signal system,
704, 722: right time signal system, 708: strength re-panning system
712: Composite signal generation system, 714: Power compensation system

Claims (20)

A system for generating parametric stereo data from phase modulated stereo data, the system comprising:
The left channel audio data and the right channel audio data, and based on the phase difference between the left channel frequency domain data generated from the left channel audio data and the right channel frequency domain data generated from the right channel audio data, A phase difference system for generating phase difference data, wherein the left channel frequency domain data includes left channel amplitude data and left channel phase data and the right channel frequency domain data includes right channel amplitude data and right channel phase data , The phase difference system;
A phase difference weighting system for receiving the phase difference data and generating weighted data for adjusting the left channel amplitude data and the right channel amplitude data based on the phase difference data; And
Adjusting the left channel amplitude data and the right channel amplitude data using the weighted data, removing the left channel phase data from the left channel frequency domain data, and removing the right channel phase data from the right channel frequency domain data Amplitude change system
And generating a stereo stereo data stream. 2. The system of claim 1, wherein the phase-difference weighting system receives a plurality of frames of left channel frequency domain data and right channel frequency domain data. 3. The apparatus of claim 2, further comprising a buffer system for storing the phase difference data between the left channel frequency domain data and the right channel frequency domain data for two or more corresponding frames of left channel frequency domain data and right channel frequency domain data,
Wherein the system is further configured to generate the parametric stereo data. The apparatus of claim 3, wherein the phase difference weighting system receives phase difference data for a first corresponding frame and a second corresponding frame of left channel frequency domain data and right channel frequency domain data, and outputs left channel frequency domain data and a right channel frequency Determining a first phase difference between the first corresponding frame and the second corresponding frame of the area data,
Wherein the phase difference weighting system receives phase difference data for a second corresponding frame and a third corresponding frame of left channel frequency domain data and right channel frequency domain data and outputs phase difference data for the left channel frequency domain data and the right channel frequency domain data, And determines a second phase difference between the corresponding frame and the third corresponding frame. 5. The method of claim 4, wherein the phase difference weighting system generates weight data to adjust the left channel amplitude data and the right channel amplitude data based on the first phase difference and the second phase difference. A system for generating stereo data. delete 3. The method of claim 1, further comprising: receiving left channel frequency domain data from which the left channel phase data is removed and right channel frequency domain data from which the right channel phase data is removed from the amplitude changing system, A frequency domain to time domain transformation system for transforming right channel frequency domain data into amplitude adjusted left channel time domain data and amplitude adjusted right channel time domain data;
Wherein the system is further configured to generate the parametric stereo data. 2. The method of claim 1, wherein the phase difference system comprises the following algorithm:

To-
here,
P = phase difference between left channel and right channel;
X _l = left stereo input signal;
X _r = right stereo input signal;
m = current frame; And
K is a frequency bin index. ≪ RTI ID = 0.0 > A < / RTI > A method for generating parametric audio data from phase-modulated audio data,
Converting first channel audio data from a time domain signal to first channel frequency domain data, wherein the first channel frequency domain data comprises first channel amplitude data and first channel phase data; Channel audio data conversion step;
Transforming the second channel audio data from the time domain signal to the second channel frequency domain data, wherein the second channel frequency domain data comprises the second channel amplitude data and the second channel phase data. Channel audio data conversion step;
Determining a phase difference between the first channel frequency domain data and the second channel frequency domain data;
Determining weighted data for applying to the first channel amplitude data and the second channel amplitude data based on the phase difference between the first channel frequency domain data and the second channel frequency domain data;
Adjusting the first channel amplitude data to the weighted data;
Adjusting the second channel amplitude data to the weighted data;
Removing the first channel phase data from the first channel frequency domain data; And
Removing the second channel phase data from the second channel frequency domain data
≪ / RTI > 10. The apparatus of claim 9, wherein the first channel frequency domain data comprises a first plurality of frames and the second channel frequency domain data comprises a second plurality of frames,
Wherein the phase difference is determined between two or more corresponding frames of the first plurality of frames and the second plurality of frames. 11. The method of claim 10, wherein the weighting data is determined based on a phase difference between the first plurality of frames and two or more corresponding frames of the second plurality of frames. Way. delete 10. The method of claim 9, wherein determining the phase difference comprises:

, The method comprising:
here,
P = phase difference between left channel and right channel;
X _l = left stereo input signal;
X _r = right stereo input signal;
m = current frame; And
K is a frequency bin index. delete delete delete delete delete delete delete

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